Documents of the kind mentioned initially herein are known especially from Swiss patent 661 602. To produce such value documents, embossed foils, especially hot-embossed foils, can serve as described for example in German patent document 34 22 910 C1.
Known documents or embossed foils have a structure serving as a security attribute above all against color copying and effective in an optical diffraction sense, the optically diffractive, i.e. light-reflecting diffractive and/or refractive structure having the basic advantage that it can be recognized by the unaided eye but also can be machine read. Typical of such structures are those which are applied to bank notes and are, inter alia, kinegrams and pixelgrams. The falsification of such structures is very difficult but nevertheless can be carried out when it is possible to free the structured surface from the document and galvanically reproduce it utilizing the original as a model or to copy it by photographic techniques.
To make documents secure against falsification, the use of luminescent layers in the documents has been proposed. German patent document DE-OS 37 41 179 discloses the use of two security attributes, namely, one embossed in the paper and thus providing a sensible relief, and further, as a second security attribute, luminescent substances upon the crests or in the valleys of the relief. According to German patent document DE-OS 37 41 179 use is made of a transfer band whose layers are applied by an adhesive layer upon the document, the transfer band containing a color layer of a luminescent material but also in addition to this luminescent layer a color pigment layer.
German patent document DE-OS 39 06 695 shows embedding of a strip in a document as a security element. The strip is comprised of a light-permeable plastic foil which is provided with indicia or patterns in the form of recesses whereby additionally luminescent substances are disposed in regions which are equal in coverage to the recesses. In this case, two security elements are provided, namely one formed by the indicia and patterns while the other is formed by the luminescent substances.
German patent document DE-PS 27 54 267 documents with two security attributes and which have luminescent characteristics. By contrast with brilliant surface optical markings, here there are threads, platelets and fibers embedded in the paper.
The state of the art which has become known, can be summarized by saying that it is known to apply luminescent substances on the one hand in use regions of nonoptical features by (partial) printing, coating, embossing or also by transferring strip applications and, on the other hand, in use regions of the optical means (for example reflective grid structure with line counts of about 100/mm and line depths of about .mu.m), for securing documents with surface-covering protective layers.
In earlier thinking with respect to machine detection of optical features generally there has been a concentration upon the closely related optical reading of the grid structure or the information or image content, which has been associated not only with a substantial technological expense for the reading of multidimensional information, but also the effects of damage which can arise in bank note circulation and which can lead to destruction of the structure and requires taking into consideration the disadvantage that unreadability of the authenticity features may arise. Also, corresponding impression falsification of the optical attribute cannot be recognized by such detection.